FEEDING ECOLOGY AND FOOD COMPETITION OF THREE DEMERSAL FISH SPECIES IN THE COASTAL WATERS OF SHANDONG PROVINCE

The coastal water of Shandong Province is a typical continental marginal sea, which is an important fishing because of its unique geographical environment and hydrological factors. It is also a major spawning ground and feeding ground for many fishery organisms in the Yellow Sea. In recent years, due to the high fishing intensity, fishery resources had declined seriously. The proportion of traditional economic species in the catch has decreased significantly, and the fish community structure has changed greatly. By studying the feeding ecology and food competition between fish species in Shandong offshore waters, this study aims to understand the effects of interspecific competition on the spatial distribution, population change and stability of fish community. It will also provide basic information for the management and sustainable utilization of fishery resources in this area. Based on the data of seasonal bottom trawl surveys and stomach content analysis from 2016 to 2017, the food composition and differences in trophic and spatial niche of Cleisthenes herzensteini, Lophius litulon and Chelidonichthys spinosus were analyzed by assessing niche overlap coefficient and classification tree. A total of 1630 samples were collected, of which 440 were empty stomachs. The adequacy of stomach sample size was determined by cumulative prey curves. Through the cumulative prey curves, it was found that the curves of three demersal fish species were all close to an asymptotic line, indicating that the number of stomachs was sufficient to reflect their feeding ecology. The results showed that the three demersal species were benthic predators, mainly feeding on shrimp and fish. Among them, C. herzensteini mainly fed on shrimp (61%) and echinoderms (12%), C. spinosus mainly fed on shrimp (68%), while L. litulon mainly fed on fish (66%) and shrimp (26%). There were some differences in the feeding ecology of them, which could be distinguished by building a decision tree. ANOSIM analysis also showed that the interspecific differences in feeding ecology of the three fish species were greater than the intraspecific differences. Canonical correspondence analysis (CCA) was conducted to study the main factors affecting feeding ecology. Bray-Curtis similarity index was used as the basis of matrix calculation. Length, weight, season and geographical location (latitude, longitude) were selected as explanatory variables. A biplot of response variables and prey groups along the first two canonical axes was constructed for interpretation. The result of canonical correspondence analysis (CCA) showed that the feeding ecology of C. herzensteini was mainly related to its length. As length increases, C. herzensteini feed on more fish and shrimp. The feeding ecology of C. spinosus was mainly related to the season, while the feeding ecology of L. litulon was mainly affected by the spatial distribution. L. litulon eat more shrimp at the high latitude areas, and they feed on more fish with the increase of longitude. By calculating the spatial and trophic niche breadth of three fishes, it was found that C. herzensteini had the lowest trophic niche breadth, indicating that the prey diversity of C. herzensteini was low. The spatial niche breadth of L. litulon was the highest, indicating that its ability to adapt to the environment is relatively high, which is also consistent with its wide distribution in Shandong offshore waters. The trophic-spatial two-dimensional niche overlap index reflected the similarity in the utilization of food and spatial resources among species. If the overlap index of any dimension decreases, it would lead to the decrease of trophic-spatial two-dimensional niche overlap index. The trophic niche overlap coefficient of three fish species was high, but the spatial niche overlap coefficient was low, which reduced the interspecific competition to a certain extent.